CHAPTER 13 - SPECIAL MEASUREMENT METHODS IN OPEN CHANNELS
9. Weir Sticks
Weir sticks are commercially calibrated stick or staff gage type devices which may be placed by hand upon the crest of a weir. In principle, the sticks show depth of flow plus velocity head or the runup of water above the water surface at the weir blade. This device gives an indication of the head that would have been measured at conventional weir measurement stations. Readings are taken at the top of the runup of water to indicate the rate of flow. Some sticks contain a piezometer and manometer to average the pulsations in the head reading. Turning the stick to an angle will not improve accuracy unless the stick has been calibrated in this position.
At best, the sticks can only approximate the potential accuracy of weirs when head is carefully measured in the normal manner. Weir sticks are designed to measure unit discharge along the crest of rectangular suppressed weirs. Thus, the gage indicates the discharge per unit length of weir. The design intent was to make weir measurements simpler without need for staff gage zero setting. Also, poor distribution of velocity of approach at the crest could be accounted for by multiple stick measurements and averaging along the crest because the weir stick measures the depth on the crest and the corresponding velocity head. Thus, they compensate for velocity of approach, such as caused by sediment deposits ahead of the weir blade.